Abstract:

Feasibility and construction of closed loop winding tightness controller was studied. Both basic PI-controller and LQR state feedback controller were applied. The controllers were tuned and tested in winding simulations and in pilot winder trial runs. The chosen feedback variable was the web thickness or strain in the roll radial direction measured by means of the density measurement. The controller output was the Wound On Tension, which was converted to the winder control variables, nip load, web tension and winding force, by means of the inverted nip model. The nip model was constructed as the experimental response surface model. The nip model data was measured in the pilot winder with several different winder reference values and web speeds and the response surface model was fitted to the data by means of the least squares method. The experimental nip model was inverted and used as a component in winding control and simulation. Two theoretical nip models were reviewed and compared to the experimental nip model. The density measurement was implemented with a novel algorithm based on the time varying least squares method. The Wound On Tension measurement was done by means of the indirect method, which uses the roll deformation data from the density measurement and the wound roll stress model. The method was improved compared to the earlier implementations by using the large deformations total stress version of the wound roll model augmented with the viscoelastic material model and the centrifugal forces. A new method for indirect web calliper measurement was introduced based on the roll model and radial deformation data. The various versions of the wound roll stress models were implemented and their results compared. The total stress version was found to be suited for the Wound On Tension measurement from the radial deformation measurement data. The algorithms were tested with pilot winder trial runs with two printing paper grades, the LWC paper and the Newsprint paper. The computed radial pressures were verified with the direct pressure measurements.